It is late, and the house is quiet. Then something pops inside a wall, and a little later a board creaks in the hall. Reports of hauntings include seeing a figure, odd smells, sudden changes in temperature and a strong sense of presence. The Society for Psychical Research was founded in London in 1882 to study such reports with care. Let's look for what made a pop or a creak, starting with the house itself.
Houses make creaks and pops, and wood floors and pipes make them. Think about the materials a house is made from and what happens to them over a day and a night. Wood, metal and glass get a tiny bit bigger when they warm up and a tiny bit smaller when they cool down. A house warms up and cools down, and the things in it change size a little each time, so each time is a chance for a pop.
Winter brings its own noises. Winter air dries wood out, so the boards shrink. That is why some floors make more noise in cold weather. Wood floors can creak more in winter because dry air makes the boards shrink and pull apart a little, so a floor that was quiet in summer can start to creak when the cold comes.
Two more clues can be found in the walls and around the windows. Metal air ducts can pop when they warm up, so a pop in the wall is worth tracing to a duct. A draft is something else: moving air that slips in through gaps around windows and doors. Each of these clues can be checked one at a time, and each is a place where a person can look.
Not every sound is one you can hear. People generally hear sounds between 20 and 20,000 hertz. Infrasound is sound with a pitch below 20 hertz, lower than the sounds people usually hear. Pitch is how high or low a sound is. A house at night may seem quiet, but sound has a whole range of pitches, and infrasound sits below the range that people generally hear.
Now for what the eyes see in the dark and in the daytime. People see faces in clouds, rocks and tree bark. Our brains are very good at spotting faces. Seeing faces in things that have no faces has a name: pareidolia. The brain area that notices faces gets busy when we only think we see a face, like one in a cloud. So when a face seems to look back from a cloud or from tree bark, the brain area that notices faces is part of the story.
One famous face is on another planet. In one old photo, a hill on Mars looked like a face, and the reason was shadows. Then sharper photos came, and they showed that it is just a hill. There are dozens of hills like it nearby, so the hill with the face is only one of many. Sharper pictures gave a clearer look, and a clearer look is what settled the question.
Shadows can play tricks on a mountain too. On a mountain, your own shadow can fall on fog or cloud below you. A mountain climber's shadow on cloud can look huge and have a colored ring around it. It is only the climber's own shadow. A pop, a creak and a shadow each have something that can be checked, and that is a good way to meet a spooky feeling: with a question about what made it. Next time you hear a pop in the night, you will have a list of clues to check.
Words to know
- pareidolia: seeing faces
- infrasound: very low sound
- ducts: air tubes
- draft: moving air
